Gear shaping is a cutting process wherein a gear of a desired tooth profile with cutting capability can generate the similar tooth profile in a workpiece, i.e. a “blank”, mounted on a work table. Gear shaping can be used to generate a tooth profile on the outer periphery of a workpiece, or the inner periphery of the workpiece. Additionally, gear shaping is particularly advantageous when shaping gears having a shoulder, i.e. a secondary flange, below the inner or outer periphery containing the tooth profile and in close proximity thereto.
As it relates to the general state of the art, reference can be had to U.S. Pat. Nos. 3,628,359; 4,136,302; 4,254,690; 4,533,858; 4,542,638; 4,629,377; 4,784,538; 5,345,390; and 7,097,399, the entire disclosures of which are also hereby incorporated by reference in their entireties. As can be generally appreciated from the above, gear shaping is a cutting process wherein a spindle fixedly carrying the cutting gear linearly and vertically reciprocates across the inner or outer periphery of the workpiece to successively cut the desired tooth profile. The cutting gear and workpiece also rotate relative to one another during cutting in the same manner that the finished gear would mesh with its mating gear during operation.
The linear reciprocation, i.e. stroking, of the spindle is typically accomplished by a conventional rotary motor and crankshaft linkage commonly referred to as the stroke drive. The rotary motion of the motor is converted to linear stroking motion by way of the crankshaft and linkage. The motor is typically statically mounted on a frame of the gear shaping machine, and the crankshaft and linkage are connected to the spindle.
The rotary motion of the spindle is also typically accomplished by a conventional rotary motor and linkage distinct from the stroke drive and commonly referred to as the rotary drive. This rotary motor is also statically mounted on a frame of the gear shaping machine in a like manner as the rotary motor providing linear reciprocation. The motor is mechanically linked to the spindle by the linkage, and is responsible for rotating the spindle to effectuate the desired rotary feed, i.e. meshing, of the cutting gear and the workpiece.
During a single stroke cycle, the spindle undergoes both linear and rotational motion. More specifically, the spindle is driven linearly toward the workpiece mounted on the work table during a cutting stroke by the stroke drive. After performing a cut, the cutting gear is then backed away from the workpiece in a back-off motion along a radial axis so as to not make contact with the workpiece during a return stroke. The spindle is then driven linearly away from the workpiece in a return stroke generally opposite the cutting stroke, also by the stroke drive. Generally, cutting does not occur during the return stroke. The cutting gear then moves along the radial axis in an opposite manner as the back-off stroke to then begin another stroke cycle. The spindle and the cutting gear rotate continuously during both the cutting and the return stroke by way of the rotary drive. Similarly, the work table and the workpiece continuously rotate during the cutting and return stroke by way of a work table drive.
Unfortunately, several problems arise as a result of the design of contemporary gear shapers discussed above. First, contemporary stroke drive design presents several problems. Separate additional motors and axes of control are required throughout the crankshaft linkage between the motor and the spindle to adjust stroke position and stroke length. Additionally, backlash is inherently present in crankshaft type linkages, and must be compensated for.
Second, due to the static placement of the motor of the rotary drive, a lead guide is ordinarily required to maintain the straightness of the spindle during the rotation thereof as the spindle reciprocates. Even in more contemporary CNC systems, some type of lead guide is still required to maintain the straightness of the spindle and transmit the rotational motion and force from the rotary drive. The lead guide is essentially a sliding joint between the statically mounted rotary motor, the linkage extending therefrom, and the spindle.
Third, as noted above, the spindle continuously rotates as it reciprocates. The spindle also backs away from the workpiece in a back-off stroke prior to the return stroke. However, the spindle, and more particularly the cutting gear attached to the spindle, can interfere with a trailing flank of the workpiece during the return stroke despite the back-off stroke causing a condition known as rub. Rub is a function of the continuous rotary feed rate of the cutting gear and the workpiece, as well as workpiece and cutting gear geometries.
In view of the above, it is therefore desirable to have a cutting machine for gear shaping that alleviates one or more of the above noted deficiencies currently in the art and/or that provides other advantages or features.